leetcode138

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138. Copy List with Random Pointer

Description

A linked list is given such that each node contains an additional random pointer which could point to any node in the list or null.

Return a deep copy of the list.

Idea

Clone problem is always involved with hashmap which store the mapping from original nodes to new nodes.

Code

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# Definition for singly-linked list with a random pointer.
# class RandomListNode(object):
#     def __init__(self, x):
#         self.label = x
#         self.next = None
#         self.random = None

class Solution(object):
    def copyRandomList(self, head):
        """
        :type head: RandomListNode
        :rtype: RandomListNode
        """
        if not head:
            return None

        # copy node (label) and create the mapping
        cur = head
        map_ = {}
        while cur:
            map_[cur] = RandomListNode(cur.label)
            cur = cur.next
            
        # traverse raw list and copy the relation (next and random)
        cur = head
        while cur:
            if cur.next:
                map_[cur].next = map_[cur.next]
            if cur.random:
                map_[cur].random = map_[cur.random]
            cur = cur.next
        
        return map_[head]